The woman is a preschool teacher, said Detective Sgt. Brian Spears, commander of the San Jose Police Department’s Internet Crimes Against Children Task Force. “She’s definitely a hero in our eyes,” he said.

Kellar was charged with attempted child molestation and solicitation of a sex crime, both felonies. He was arraigned on Thursday and was being held without bail at the Santa Clara County Jail.

Police named Gail Burnworth, 50, also a resident of Tacoma, as the person Kellar was suspected of texting. They have also located two children, ages 5 and 7, who may have been victims of sexual abuse.

Sergeant Spears said the text messages “described specific sex acts performed on children, as well as bestiality.”

“It definitely goes beyond just that flight,” he added. “There is a history of conversations between them.”

According to a statement from the city of Seattle on Wednesday, it seems that Burnworth had access to the children. She was arrested in Tacoma on July 31 but was released after prosecutors did not formally charge her within 72 hours.

She was arrested again on Friday night on a federal warrant for conspiracy to produce child pornography.

Southwest Airlines did not provide access to the crew member who alerted police because of the criminal investigation. In an emailed statement, it said, “We always encourage customers to say something to our employees or law enforcement if they see something suspicious.”

The authorities in California and Washington said federal charges are likely, and the F.B.I. was involved in the continuing investigation.

Capt. Mike Edwards, commander of the Seattle Police Department’s Internet Crimes Against Children Task Force, said the two children who may have been victims remained at their home with their parents.

Police did not identify the teacher who reported the text messages. “We’re very grateful that she was on that plane,” Edwards said.

“I think the big message and the big takeaway on this is, for all of us, is to pay attention to what’s going on around you,” he said. “You never know how important it could be.”